Diesel engine operation involves combustion that generates exhaust gas. During combustion, an air/fuel mixture is delivered through an intake valve to cylinders and is combusted therein. After combustion, the piston forces exhaust gas in the cylinders into an exhaust system. The exhaust gas may contain diesel particulates generally characterized as soot.
A diesel particulate filter (DPF) can be used to reduce the level of soot in the exhaust gas. The DPF typically includes a separation medium and an inner cavity having small pores that capture soot. Exhaust gas flows through the pores and soot accumulates on the walls. As the accumulation increases, exhaust flow may be blocked and pressure increases inside the DPF. The DPF can be regenerated using microwave radiation to burn off soot and allow the flow of exhaust gas to reduce pressure. DPFs may be coated with a magnetic microwave absorbing material, such as ferrite, to concentrate microwave absorption in areas where soot accumulates.
Microwave systems used to regenerate DPFs typically include a microwave source and a power supply. Microwaves are directed into the DPF cavity and are absorbed by the absorbing material. Heat from the microwaves causes the temperature of the absorbing material to increase, thereby causing accumulated soot to combust. Once combusted, heat from a small amount of soot is leveraged to burn a larger amount. When the temperature of the absorbing material exceeds a Curie temperature, the material loses the ability to absorb. Microwaves that are not absorbed are reflected back toward the microwave source and are dissipated as heat.